1. Field of the Invention
This invention relates generally to an apparatus providing a signal indicating the position of a shaft for a valve or like devices, and more particularly, to a housing for a switch device, a shaft position indicating mechanism incorporating a visual display of the shaft position, and a mounting assembly for mounting the switch device to a rotary valve or a linear valve, and/or actuators.
2. Description of the Prior Art
In general, electrical switch means are used for various applications such as in fluid or other flow systems. One particular application is in a flow line for monitoring and regulating the condition of a rotary or linear valve and/or actuator (i.e. open or closed) and/or to control the opening or closing of successive valves in the flow lines as a function of the preceding valves. The prior art included electrical switches that are mechanically activated in response to this operative state of the valve.
These mechanically actuated switches are frequently subjected to severe environmental conditions, including dust, moisture, or other corrosive or explosive foreign matter. Such adverse environmental conditions have a deleterious effect on the electrical switches and over a period of time may lead to switch malfunctioning causing erroneous indicator and control signals.
Attempts have been made to solve the problems associated with prior art devices, particularly for rotary valves. U.S. Pat. No. 4,214,133 provides a rotary shaft position indicator and control in which microswitches are enclosed within a housing that is sealed against the introduction of adverse matter. The microswitches are activated by a magnetic coupling through a wall of the housing. Even though a sealed switch cavity is provided, the switch and switch activating structure requires many mechanical components.
A less complex structure for a rotary shaft position indicator with a sealed switch cavity is disclosed in U.S. Pat. No. 4,831,350. This device utilizes magnetically actuated reed switches. A cylindrical dome houses the reed switches. The dome screws onto a secondary housing member and the reed switches are screwed to the secondary housing member. An external switch actuating structure comprises a magnet holder mounted to the housing for rotation with the rotary shaft. The entire dome assembly with the switch actuating device is mounted on the shaft of a rotary valve.
Both U.S. Pat. Nos. 4,214,133 and 4,831,350, as well as other valve position sensing devices of the prior art, lack means for visibly displaying the orientation of the rotary shaft.
Such an attempt was made in the disclosure of U.S. Pat. No. 4,962,290. The base is designed to support a flared drum on the outer surface of which are graphic characters indicating an "open" or "closed" position. The "open" and "closed" position of the rotary shaft is viewable through a window on a fixed indicator cover and visible from the above and the sides. One drawback with the devices of U.S. Pat. Nos. 4,214,133 and 4,962,290 is the difficulty involved in mounting and replacing the switches which are actuated by cam elements mounted on a rotary shaft in alignment or connected to the rotary valve shaft. Another drawback to the shaft positioning sensing devices of the aforesaid patents is that the cavity sealing effect is broken when the switches are to be adjusted and/or replaced, that is, the dome cover must be removed.
Still another problem with the prior art shaft indicators relates to the inability to adapt to either a rotary valve or a linear valve found in the field with which the indicators are to be used.
A still further problem with the prior art is that the electrical switches are preferably for low voltage and low current applications such as the reed switches of U.S. Pat. No. 4,831,350.
A still further problem with the prior art is that the shaft of the valve protrudes through the enclosure of the shaft position indicating mechanism. This results in sealing of the shaft being difficult to achieve, costly, and subject to leaking. Additionally, there are very stringent requirements on rotary shaft seals for explosive proof devices.
There is further lacking in the prior art a design for a valve position sensing and/or indicating device which eliminates the guess work and labor involved in replacing the switches in the assembly. There is further lacking in the prior art a valve position sensing and/or indicating device, which is compact, relatively small, and which does not interfere with other devices on the valves.